Cryptococcus neoformans is an encapsulated fungus, and is the etiological agent of human cryptococcosis. This fungal pathogen represents an opportunistic organism and mainly infects immuno-compromised and immuno-competent individuals. There are roughly 0.4-1.3 cases per 100,000 per year in the general population. Among AIDS patients, however, the annual incidence is 200-700 cases per 100,000. The species Cryptococcus neoformans is composed of three variants; namely Cryptococcus neoformans v. gattii, Cryptococcus neoformans v. grubii, and Cryptococcus neoformans v. neoformans. The grubii and neoformans variants have a worldwide distribution and are often found in soil which has been contaminated by bird excrement. Infections are typically acquired by inhalation of the desiccated fungal cells known as basidiospores. Primary infection with Cryptococcus neoformans is thought to be common early in life where the disease can either lie dormant in the lungs or disseminate to the central nervous system. With pulmonary disease, the infection may be acute or chronic. If the fungal pathogen is able to disseminate, infection can present itself as meninogencephalitis, cutaneous lesions, and other inflammatory symptoms.
Conventional detection methods for Cryptococcus neoformans include culture on fungal media, colony morphology and nutritional characteristics. Fungi (such as Cryptococcus neoformans) may take 2-3 days or even weeks to grow in culture. This makes timely identification difficult and greatly impairs efficient treatment where rapid identification of fungal genus/species is required. Most of these methods are either time-consuming, laborious, or provide inconclusive results.
U.S. Pat. Nos. 5,464,743, 5,580,971, 5,763,163, 5,763,169, 5,707,802, and 6,180,339 disclose detection of fungus including Cryptococcus neoformans using a PCR assay to detect ribosomal RNA (rRNA). The designed probes are targeted against 28S rRNA. U.S. Pat. No. 6,180,339 describes amplification of a 401 bp fragment spanning the large subunit rRNA/intergenic spacer region. This PCR-based assay has limitation because of its lack of specificity. Multiple probes may be required to distinguish among fungal species.
U.S. Pat. No. 5,919,617 discloses, besides immunological means, the use of primer pairs to amplify the saccharopine dehydrogenase gene to detect Candida albicans. 